Welcome to the Real World of Lead Free Soldering

Transcription

1 Welcome to the Real World of Lead Free Soldering Metallic Resources, Inc. Howard Stevens Nimal Liyanage,, Ph.D

2 Objective: to Provide Education Regarding the Effects of Various Lead Free Soldering Alloys used in Assembly Operations on Available Board Finishes used in PC Board Fabrication.

3 Prime Importance to Circuit Board Fabricators: Board Finish Selection. Cost. Shelf Life. Process Changes and Parameters. Demonstrated Solderability.

4 Prime Importance to Circuit Board Assemblers: Alloy Selection. Cost. Wetting and Wicking Capability. Process Changes and Parameters. Demonstrated Solderability.

5 Primary Board Finish Purpose: To prevent Oxidation of the Copper Traces, Pads, and Through Holes, in Order to Preserve Solderability.

6 When Coating Bare Boards Different Finishes Lose Solderability at Different Rates. Solderability will Deteriorate Over Time. Longer Storage Time Equals Less Solderability.

7 Available Board Finishes: Lead Free HAL. Immersion Tin. Immersion Silver. ENIG. OSP.

8 Immersion Tin: Process Dependent with Relatively High Cost month Shelf Life? Thickness limited to less than 1 micron (Average of microns). Loss of Solderability when Forming Intermetallics with Copper.

9 Immersion Silver: Process Dependent with Relatively High Cost month Shelf Life? Thickness limited to less than 1 micron (Average of microns). Loss of Solderability when Silver has Diffused into the copper. Potential for Tarnishing.

10 ENIG (Electroless( Nickel Immersion Gold): Higher Cost. Thickness limited to less than 1 micron (Average of microns). More Difficult to Solder to. Introduces Gold into the Solder Pot which may Cause a more Brittle Solder Joint. Process can go Awry more Often than HAL, requiring replacement of Chemicals.

11 OSP (Organic Solder Preservative): Limited Shelf Life. Works better with High Activity Fluxes. Temperature Dependent. Thickness limited to less than 1 micron (Average of microns).

12 Hot Air Leveling: The most Cost Effective. Yields the Best Solderability of the PCB. Yields an Excellent, Long Shelf Life (1 to 1.5 years) no Different than Sn63/Pb37.

13 Hot Air Leveling: Compatible with Wave Soldering, SMT, Selective Soldering. Existing Equipment Historically Geared to Hot Air Leveling. Solderability Confirmed by Visual Inspection.

14 Many Lead Free Alloys Considered for Board Fabrication, Wave, SMT, and Selective Soldering.

15 Some Guidelines in Alloy Choice: Melting Point was not as Important as was First Thought. Adjust the Process to Compensate (somewhat Higher Solder Pot Temperatures will be Necessary).

16 Alloy Choices for Fabrication and Assembly: Antimony (Sb( Sb) ) and Bismuth (Bi) Eliminated due to Brittle Solder Joints and Finishes. Adding Zinc (Zn) Creates a Dull, Elastic Finish, which Leaves

17 Alloy Choices for Fabrication and Assembly: Sn96.5/Ag3.0/Cu0.5 (SAC Alloys) Sn99.3/Cu0.7 Eutectic Sn99.5/Cu0.5/Ni0.5 Sn99.5/Cu0.5/Co

18 A Binary Alloy is Preferable to a Tertiary Alloy Because it is: Easier to Keep the Solder in Spec for Both PC Fabrication and PC Assembly Operations. Lower in Cost.

19 SAC Alloys: Advantages: Readily Accepted by Industry, Lower Melt Point Compared to Sn/Cu Alloys. Disadvantages: Higher Cost, Limited Longevity Studies, Dull Crystalline and Grainy Solder Joint, Higher Melt Temp., Poorer Through-Hole Fill, Potential for Stainless Steel Corrosion, Poor Coplanar Surfaces in HAL, Tertiary Alloy.

20 Sn99.3/Cu0.7 Eutectic: Advantages: Lower in Cost, Binary Alloy. Disadvantages: Higher Melt Point (228 C C Compared to 183 C C for Sn63), Duller Crystalline Finish, No Longevity Studies, Corrosion in Stainless Steel Solder Pot?

21 Sn99.5/Cu0.5/Ni0.05: Advantages: Brighter, Shinier Board Finish and Smoother, more Flat Surface. Disadvantages: Higher Melt Point (228 C C Compared to 183 C C for Sn63), Limited Longevity Studies, Corrosion in Stainless Steel Solder Pot? Patented Alloy Results in Higher Cost.

22 Sn99.5/Cu0.5/Co: Advantages: Lower Cost. Smoother, Uniform Flat Surface. Brighter, Shinier Board Finish and Solder Joint, no Joint Cracking or Solder Voids, Binary Alloy. Disadvantages: Higher Melt Point (228 C C Compared to 183 C C for Sn63, 217 C C Compared to SAC305), Limited Longevity Studies, Corrosion in Stainless Steel Solder Pot?

23 Sn99.5/Cu0.5/Co: The Addition of Grain Refining Trace Elements such as Germanium, Nickel, Silver and Cobalt will Overcome Many Disadvantages of Sn/Cu and SAC Alloys.

24 Sn63/Pb37 Bottom Side Fill:

25 Sn99.5/Cu0.5/Co Bottom Side Fill:

26 Sn99.5/Cu0.5/Co Top Side Fill:

27 Testing of Various Alloys. Physical Properties: SAC305 Sn/Cu/Co 63/37 Melting Point ( 0 C) Density (g/cm 3 ) Operating temp.( 0 C) Tensile Strength (M Pa) Elongation

28 Testing of Various Alloys. Physical Properties: SAC305 Sn/Cu/Co 63/37 Thermal Conductivity (J/m s K) Electrical Resistance (µώm)) Thermal Shock (-40/+80 C Each 1 Hr) 1000 Cycles 1000 Cycles 500 Cycles

29 General Wetting Characteristics:

30 General Wetting Characteristics:

31 Testing of 250 C: : Wetting

32 Testing of Sn99.5/Cu0.5/Co: : Wetting

33 Comparison of WB Tests: Sn63/Pb37 Sn/Cu/Co Alloy Temp. 0 C Max Wetting Force 0.32 >0.31 (mn/mm) Time to achieve max wetting Force (sec) Av. force at sec

34 Wetting Comparison: For the Sn63 solder, wetting was instan- taneous,, rising to maximum wetting force in seconds. Maximum wetting force was 0.32mN.mm of wettable length. For the Sn99.5/Cu0.5/Co at 265 and 275 C, the wetting was also instantaneous. The rate of rise is uniform, near textbook, and the maximum wetting force is very slightly lower at 0.31mN/mm.

35 Spread Comparison: : Sn63/Pb37

36 Spread Comparison: : Sn63/Pb37

37 Spread Comparison: : SAC305

38 Spread Comparison: Sn/Cu/Co

39 Spread Comparison:

40 Wetting/Spread Test Results: ENIG Showed Poor Wetting. Sn63 gave 20% more Spread than SAC305 and Sn/Cu/Co Pastes. Immersion Silver Showed Poor Wetting with all Pastes.

41 Wetting/Spread Test Results: OSP Showed Poor Wetting with Sn/Cu/Co and SAC Alloys. Sn63/Pb37 was 30% Better in Wetting and Spread. Immersion Tin Showed Total Diffusion of Sn63 through the Tin Coating onto Underlying Copper. Also Evidence of Intermetallics at the Outer Edges of the Spread.

42 Wetting/Spread Test Conclusions: HAL Provided the Best Overall Wetting no Matter what Paste was Used. The Sn/Cu/Co Alloy Wets as Well as the SAC305 Alloy, therefore the Low Cost of Sn/Cu/Co becomes Much More Important.

43 Wetting/Spread Test Conclusions: Immersion Silver Exhibited the Poorest Wetting and Spread Across the Board. ENIG and OSP were a Little Better with Sn63/Pb37 Pastes.

44 Average Comparative Spread of All Alloys: 100.0% 95.5% S p r e a d P e r f o r m a n c e 95.0% 90.0% 85.0% 80.0% 87.2% 82.5% 83.8% 89.6% ENIG ImAg OSP ImSn HAL 75.0%

45 Average Spread of Water Soluble SAC305 vs. Sn/Cu/Co: % S p r e a d P e r f o r m a n c e 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% % 0.0% SAC305WS Cobalt995WS

46 Average Spread of No Clean SAC305 vs. Sn/Cu/Co: S p r e a d P e r f o r m a n c e 100.0% 90.0% 80.0% 70.0% 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% SAC305NC Cobalt995NC

47 Results of SAC305 vs. Sn/Cu/Co Comparison: No Significant Differences in Wetting or Spread Between the Two Alloys.

48 Testing of Sn99.5/Cu0.5/Co: Copper Thickness Reduction: Number of Passes Copper Thickness (Avg.) mils Variation From Original Copper Thickness (mils) Sn99.7Cu0.3/Co Sn63 Sn99.7Cu0.3/Co Sn

49 Co-Planarity Testing: Sn63/37 Panels Sn/Cu/Co Panels Panels Measured Mean µ-in µ-in. Standard Deviation 65.6 µ-in µ-in. Minimum µ-in µ-in. Maximum µ-in µ-in. Range µ-in µ-in

50 Sn99.5/Cu0.5/Co. The Addition of Cobalt Makes for a Brighter, Shinier, less Grainy Solder Finish and Joint with no Joint Cracking or Solder Voids Compared to Sn/Cu or SAC305.

51 Sn99.5/Cu0.5/Co. Electrolytic Processing with Lower Viscosity and Surface Tension Provides Improved Fluidity, and Greater Wetting and Wicking Capability for the Best Through-Hole Fill. Electrolytic Processing Reduces Re- Work (Bridging, Flagging, Cobwebbing, Icicling,, Solder Voids) at Least 30% and Joint Cracking Compared to All Other Lead Free Alloys!

52 Cost of Sn99.5/Cu0.5/Co: Little Difference Compared to Sn/Cu. Significantly Less Expensive than SAC305 for Assembly Operations. Less Expensive Compared to Other Available Board Finishes due to no Additional Processes Involved.

53 Summary: Many Board Finishes are Available and Each Works Differently for PC Fabrication. Hot Air Leveling Provides More Advantages than Other Board Finishes. Many Lead Free Alloys are Available for PC Assembly. A Binary Alloy has Advantages over a Tertiary Alloy for Wave Soldering.

54 Summary: An Sn/Cu/Co Alloy Provides the Greatest Cost Effectiveness for both PC Fabrication and Assembly Operations. Provides Excellent Solderability. Thoroughly Independently Tested.

55 Summary: An Sn/Cu/Co Alloy Provides a more Uniform Coating and Smoother Surface in HAL and the Brightest, Shiniest Solder Joints with No Grain or Voids compared to all other lead free alloys in all Assembly Operations.

56 Benefits of Partnering with Metallic Resources: Unlimited Free Pot Analysis. For Lead Free, One Analysis each Week is Recommended to Monitor Copper and Other Contaminant Levels.

57 Benefits of Partnering with Metallic Resources: Uninterrupted Supply of Product Guaranteed. Product is Stocked All Over the USA. In Case of any Catastrophe, Dual Manufacturing Locations Assure No Loss of Production.

58 Benefits of Partnering with Metallic Resources: Complete Recycling Services. Customer Audits and Tours Available at Your Request to See our Manufacturing Process in Person. (Bose, Harman Becker, Honeywell, Rockwell, etc.)

59 Thank You for Your Interest! Metallic Resources Hopes You Now Have More Information to Help Make the Critical Choices You Face.